On Aug. 2, Adam Sieminski, the administrator of the U.S. Energy Information Administration, testified that the Marcellus shale reserves may be larger than has been reported.

He told Congress: "I think it's possible we'll find, as production data begins to come in -- Pennsylvania is a state that has significant lags in reporting of production data -- we will begin to see those numbers inching up."

He testified at a hearing of the House Energy and Power subcommittee.

Sieminski's comments about a possible underestimate of Marcellus reserves is consistent with his agency's reports.

In January, the EIA estimated the Marcellus "technically recoverable resource" at 141 trillion cubic feet — that includes proved reserves plus unproven resource that it is believed existing technology could extract.

In June, the agency said that due to the fact that most producing wells are in two small areas in northeast Pennsylvania and southwest Pennsylvania-northern West Virginia, the total estimates in the Marcellus shale are highly uncertain.